1. Field of the Invention
The present invention relates to a rotary electric machine with a cooling device for cooling inside of the rotary electric machine by controlling the cooling gas flow.
2. Description of the Related Art
A rotary electric machine with a cooling device for cooling inside of the rotary electric machine by the cooling gas flow is disclosed in JP-A No. 10-42522 where a cooling fan attached to a rotor circulates cooling gas into the rotary electric machine to cool it. The size of the cooling fan is determined so as to circulate the predetermined cooling gas flow to ensure the temperature inside the machine does not exceed a predetermined limit.
On the other hand, JP-A No. 2003-284289 describes a rotary electric machine having a controller which controls the cooling gas flow forcedly circulated by a cooling fan, in response to the cooling fan inlet temperature and the load current. The controller controls a cooling gas circulation according to the temperature of gas introduced into, or exhausted from, the rotary electric machine. The control is performed based on the relation between cooling gas temperature and required cooling gas flow as obtained from measurements of an actual rotary electric machine or its machine model so that the machine temperature does not exceed a predetermined value.
In large turbine generator with a plurality of gas flow sections in the axial direction, the temperature inside the rotary electric machine may be considerably different from one point to another depending on the axial position. For example, according to the result of coils temperature analysis of the generator coils described in JP-A No. 2005-210893, the difference between the highest and lowest temperatures reaches almost 80K.
In the conventional rotary electric machine cooling system using a cooling fan which has been often adopted in turbine generators, cooling gas is circulated at a constant flow rate so that the temperature inside the machine does not exceed a limit. However this system has a problem that when the temperature inside the machine is low because of a low ambient temperature or low load ratio, the excess cooling gas flow which result in excess is circulated which lead to energy loss. Here the ambient temperature corresponds to the temperature of gas outside the generator, except the temperature of gas introduced into, or exhausted from, the generator.
On the other hand, other conventional controller controls the cooling gas flow according to the temperature of gas introduced into, or exhausted from, the rotary electric machine. However, a large scale and axially long rotary electric machine with a plurality of gas flow sections in the axial direction, the temperature inside the rotary electric machine may be considerably different from one point to another depending on the axial position and therefore, if the gas flow control is based on the temperature of gas introduced into, or exhausted from, the rotary electric machine, it is impossible to always ensure that the maximum temperature inside the rotary electric machine does not exceed a predetermined value.
In a portion of the rotary electric machine where the temperature exceeds the predetermined value, coil insulation deterioration or uneven thermal coil expansion might occur, causing damage to the coils or the core. If the cooling gas flow is determined by considering a probable temperature distribution and the temperature differences are considerable, cooling gas may be more circulated than needed in some parts of the rotary electric machine, resulting in more loss.
In case of large rotary electric machines, since the specification varies with each machine units, sufficient measurement data of the actual rotary electric machine or its machine model may not be obtained.
An object of the present invention is to provide a rotary electric machine which runs smoothly with high efficiency by adequately controlling the cooling gas flow as needed to maintain the rotary electric machine's maximum temperature below a predetermined limit.